The present invention relates to a load test stand, preferably for simulating load cycles. Particularly in the case of one axis servo systems or multi-axis servo systems, used in missiles or more specifically missile systems, a proof of the performance obtained while adhering to the specified data is required. In the case of rudder systems or wing servo systems for missiles it is necessary to determine, among other things, the actual values for the servo angle and/or the servo speed and/or the servo acceleration in both directions of motion as well as the bandwidth that is obtained for the specified load torques and inertias on the output side under all required environmental conditions. In addition, the simultaneous application of lateral forces on the output shafts of the servo system may also be required.
In order to simulate realistic load cycles for servo systems integrated into missile systems, active servo motor-driven or servo hydraulic-powered load test stands have already been developed. These load test stands can apply, as a function of the calculated requirements or closed simulation loops, realistic external load cycles on the output shafts of a servo system that is to be tested. Due to their very high overall cost and the limited adaptability of the load dynamics that can be obtained with different sizes of servo systems, these load test stands are available only on a limited scale.
Therefore, preferably simple and economical passive load test stands are used for the sole proof of the specified servo system characteristics. The structural design of these load test stands, including interfaces, can be coordinated specifically with the requirements and special features of a specific type of servo system. In this case the applications known from the prior art are based on the following principle (see FIG. 1):
A torsion bar 10 or also a combination of several interconnected torsion bars 10 are flanged to each output shaft 6 of the servo system 4 that is to be tested. In this case the torsion bar 10 injects a torque in proportion to the change in the servo angle. Inherent deviations from the linearity can be detected by means of accurate measurements of the load test stand 1. At the same time the calibration effort with respect to such measurements is very low compared to that of active load test stands. In addition, when the torsion bars 10 are clamped in a force fitted way, the conditions for zero backlash and the necessary robustness with respect to environment factors are met in compliance with the test specification.
In principle, the net weight, which is significantly less than that of active test stands, offers better conditions for combining with other test equipment, like shakers, climate chambers, etc., but which can be used to date only conditionally for other structural and mechanical reasons, which will be described below. However, the use of almost linear torsion springs assumes that, on the one hand, the spring constant, which is to be implemented by means of the design, meets the requirements of the test specification for the servo systems, and, on the other hand, that their dimensioning permits sufficiently large servo angle ranges to be covered in compliance with all of the proofs required. This last requirement is the decisive factor that defines the minimum length of the torsion bars and, as a result, the size of the entire load test stand, which in the case of multi-axis servo systems would necessitate, in particular, very large climate chambers and with respect to its suitability for vibration tests would lead to considerable structural and mechanical problems.
In theory a scaling down of the requisite servo range and, thus, the spring size could be obtained by means of different offset angles when the torsion springs are flanged to the output shaft. In this case the necessary reclamping connected with the corresponding repetition of the required temperature cycles in the climate chambers would incur an unjustifiable expense.
Therefore, some disadvantageous consequences of known, prior art test stands include the need for enormously large and powerful climate chambers as compared to the size of the servo system to be tested as well as the resulting disadvantageous structural dimensions with respect to the three axis clampability for testing under vibration load. Therefore, in the past the latter required separate test equipment, with which only one separate function can be tested without applying torsional torques. An additional application of lateral forces on the output shafts of the servo system requires connecting one or more additional devices to the test stand configuration. In this case said additional devices are not shown in FIG. 1.
Exemplary embodiments of the present invention are directed to a load test stand, which has compact dimensions while at the same time is easy and cost-effective to produce, and which makes it possible to test servo systems in a fast and reliable way.
Specifically, exemplary embodiments of the present invention are directed to a load test stand, which exhibits a passive design. The load test stand, according to the invention, comprises a frame, a flange and a spring mechanism. The spring mechanism is mounted on the frame and comprises a, preferably symmetrical, arrangement of at least four spring elements. The flange is mounted preferably by the spring mechanism. For this purpose the spring mechanism comprises frame points connecting the frame to the spring mechanism, and comprises articulation points connecting the flange to the spring mechanism. According to the invention, the flange can be coupled, by means of an adapter, to the output shaft of a servo system that is to be tested. The use of the spring mechanism, according to the invention, allows the flange to be positionable vertically and horizontally and with respect to its neutral angle position. This arrangement enables an alignment with the output shaft of the servo system in a particularly advantageous manner. Similarly the axially elastic suspension of the flange by means of the spring mechanism makes it possible to prevent preferably undefined axial forces from being introduced into the output shaft, which could be the case, for example, in the event of temperature fluctuations. Therefore, the spring mechanism acts advantageously as a compensation element. However, the use of the spring mechanism makes it possible to apply defined lateral forces to the output shaft of the servo system to be tested in a particularly advantageous manner. Therefore, the load test stand, according to the invention, can be used preferably in a very flexible way in order to test different load conditions.
In a preferred embodiment of the invention the frame points are mounted in at least one substructure. In this way the substructure and the spring mechanism form an adjustable and/or calibratable independent module. The module can be attached, preferably by means of a universal interface, to the frame. The use of the module makes it possible to create a rigid test stand, because the module can be arranged close to the servo system to be tested. As a result, the spring mechanism is situated advantageously very close to the servo system. Thus, this arrangement enables preferably the spring mechanism to be connected rigidly with zero backlash to the servo system.
It is advantageous that a prestress of the spring mechanism and/or a position of the flange along a first axis can be adjusted by means of equidirectional changes in the position of at least two frame points of the same substructure. Therefore, in a preferred embodiment the load test stand according to the invention allows the possibility of adjusting the flange to the output shaft of the servo system along a first axis.
Furthermore, it is preferably provided that a position of the flange along a second axis can be adjusted by means of a change in the opposite direction of the position of at least two opposite frame points of different substructures. At the same time the second axis is aligned preferably perpendicularly to the aforementioned first axis. Therefore, the load test stand can enable an independent alignment of the flange along two axes that are perpendicular to each other in a particularly advantageous manner.
Finally it is preferably provided that a position of the flange along a third axis can be adjusted by means of an equidirectional change in the position of at least two opposite frame points. In this context the third axis is advantageously perpendicular to the above described two axes, so that it is possible to align the flange independently along three axes.
In order to change the position of the frame points and/or the bearing points, it is preferably provided that there are actuators. The position of the frame points and/or the bearing points can be changed in an advantageous way with these actuators. Therefore, a specified load can be applied on the flange and, thus, on the servo system by means of the test stand, so that the load test stand can be used in a very flexible way. As an alternative or in addition, it is preferably provided that the frame points and/or the bearing points can also be adjusted by hand.
Furthermore, it is preferably provided that a lateral force can be applied to an output shaft, which is part of the servo system and can be connected to the flange, by changing the position of at least one frame point. Such an arrangement also allows the load test stand, according to the invention, to test the servo system for the purpose of determining how the servo system responds to lateral forces acting on the output axes. Therefore, the load test stand enables in an advantageous way a very comprehensive testing of the servo system.
In an additional preferred embodiment a spring characteristic of the spring elements can be adjusted by means of a change in the position of the articulation points and/or the frame points. In particular, the spring characteristic of the spring elements can be adjusted by changing the relative position of the frame points to the articulation points of the spring elements. Preferably the spring characteristic can be adjusted in such a way that it exhibits linear ranges. As an alternative or in addition, the spring characteristic can be adjusted in such a way that it has at least linearizable sections. It is advantageous that the spring characteristic comprises a plurality of linear and/or linearizable sections. The advantageous use of linear and/or linearizable sections of the spring characteristic allows very simple test procedures to be carried out, because the spring force and the torsional angle are in proportion to each other.
It is advantageous that the load test stand comprises a measuring system at the flange. In particular, the measuring system is designed as an angle measuring system. Such an arrangement makes it possible to measure accurately and easily the response of the servo system. Therefore, the load test stand allows a fast and easy testing of the servo system.
Preferably the measuring system in the calibrated state forms the reference for the spring characteristic of the spring elements of the spring mechanism.
Finally it is preferably provided that at least one inertial body can be coupled to the measuring system. It is particularly preferred that the inertial body be mountable in a floating manner. Therefore, the load test stand exhibits preferably inertial bodies, wherein said inertial bodies can be, in particular, simulations of rudder units or wing units, which normally would be movable with the servo system to be tested.
Furthermore, it is preferably provided that the flange, which is elastically suspended by means of the spring mechanism in the axial direction, makes it possible to compensate for tolerances axially to the output shafts of the servo system. In particular, the spring mechanism is used to compensate for the temperature-dependent changes in tolerances. In addition, it is preferably provided that other components can also be disposed on the frame, in addition to the modules. In particular, the additional components and/or the modules can be arranged at arbitrary positions around the servo system. Furthermore, it is advantageously provided that the module, in particular the substructure of the module, comprises a protective casing, a transverse guide of the spring elements, the integration of end stops and/or safety devices when coupling to and uncoupling from the output shaft of the servo system. Finally it is preferably provided that the substructure of each module can be integrated in the frame of the load test stand. The net result of this approach is an advantageous dynamic rigidity, so that multi-axis vibration tests can also be run with the load test stand.